How to show error message on rails views?


I am newbie in rails and want to apply validation on form fields.


<%= form_for :simulation, url: simulations_path do |f| %> <div class="form-group"> <%= f.label :Row %> <div class="row"> <div class="col-sm-2"> <%= f.text_field :row, class: 'form-control' %> </div> </div> </div> .....


class Simulation < ActiveRecord::Base belongs_to :user validates :row, :inclusion => { :in => 1..25, :message => 'The row must be between 1 and 25' } end


class SimulationsController < ApplicationController def index @simulations = Simulation.all end def new end def create @simulation = Simulation.new(simulation_params) @simulation.save redirect_to @simulation end private def simulation_params params.require(:simulation).permit(:row) end

I want to check the integer range of row field in model class and return the error message if it's not in the range. I can check the range from above code but not able to return the error message

Thanks in advance


The key is that you are using a model form, a form that displays the attributes for an instance of an ActiveRecord model. The <a href="https://guides.rubyonrails.org/active_record_basics.html#create" rel="nofollow">create action of the controller</a> will take care of some validation (and you can <a href="https://guides.rubyonrails.org/active_record_validations.html" rel="nofollow">add more validation</a>).

Controller re-renders new View when model fails to save

Change your controller like below:

def new @simulation = Simulation.new end def create @simulation = Simulation.new(simulation_params) if @simulation.save redirect_to action: 'index' else render 'new' end end

When the model instance fails to save (@simulation.save returns false), then the new view is re-rendered.

<h2>new View displays error messages from the model that failed to save</h2>

Then within your new view, if there exists an error, you can print them all like below.

<%= form_for @simulation, as: :simulation, url: simulations_path do |f| %> <% if @simulation.errors.any? %> <% @simulation.errors.full_messages.each do |message| %> <li><%= message %></li> <% end %> <% end %> <div class="form-group"> <%= f.label :Row %> <div class="row"> <div class="col-sm-2"> <%= f.text_field :row, class: 'form-control' %> </div> </div> </div> <% end %>

The important part here is that you're checking whether the model instance has any errors and then printing them out:

<% if @simulation.errors.any? %> <%= @simulation.errors.full_messages %> <% end %>


Do this -

<%= form_for :simulation, url: simulations_path do |f| %> <% if f.object.errors.any? %> <ul> <% if f.object.errors.each do |message| %> <li><%= message %></li> <% end %> </ul> <% end %> .......... <% end %>


You just need to add this code to the view file (myviewsnew.html.erb):

<%= error_messages_for :simulation %>

Check complete syntax of error_messages_for in <a href="http://apidock.com/rails/ActionView/Helpers/ActiveRecordHelper/error_messages_for" rel="nofollow">http://apidock.com/rails/ActionView/Helpers/ActiveRecordHelper/error_messages_for</a>


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